This invention pertains generally to the field of electronic power converters and, more particularly, to relatively low-voltage, high current power converters, e.g., for personal computer power supplies.
As the clock speed of microprocessors continues to increase, so does the demand for operating power. Operating voltages are decreasing, increasing the current necessary to meet the power demand at higher and higher levels. Standard microprocessors now have clock speeds in excess of 1 GHz, with operating voltages below 2.0 volts. The current demand for operating at these frequencies and voltages can exceed 100 amperes. In addition, current slew rates are anticipated which exceed 100 amperes per microsecond. These requirements exceed the capability of existing, mass produced computer power supplies. For example, previous attempts to stack multiphase buck converters to meet the increased current demand have largely failed to meet the slew rate requirements.
FIG. 1 shows a simple prior art power converter 50 that converts AC power from a source 40 into a controlled DC output voltage 45 using a phase angle switching controller 41 with a silicon controlled rectifier (SCR) diode 43. The SCR diode 43 operates like a rectifier with a gate that triggers conduction when the anode is positive with respect to the cathode. In particular, unless the gate of the SCR diode 43 is activated, current will not flow through it even if it is positively biased. On the other hand, once conduction is triggered, i.e., by both a positive bias and activation of the gate, the SCR 43 is latched ON and continues to conduct until the polarity reverses and the cathode is positive with respect to the anode, regardless of whether the gate continues to be activated.
The converter circuit operates as a half wave rectifier, where the input voltage (47) phase angle conduction trigger point is controlled. During a positive half cycle, when the input voltage 47 is positive with respect to ground, conduction in the SCR 43 is triggered at varying phase angles. The controller 41 senses the output voltage 45, and determines when to trigger conduction in the SCR 43 in order to keep the output voltage 45 close to a desired voltage. If the output voltage 45 sags, e.g., as a result of heavy load conditions, the controller 41 will respond by initiating conduction at an early phase angle in the input voltage 47. Conversely, if the output voltage 45 remains high, e.g., as a result of light load conditions, the controller 41 will respond by initiating conduction at a late phase angle.
FIG. 2 illustrates this concept and associated voltage wave forms. During a first positive half cycle 51 of the input voltage (47), the SCR 43 remains OFF through most of this half cycle, representing a light load condition. Conduction is triggered late, illustrated at trigger point 52 of approximately 135 degrees, and the output voltage 45 sags. During the second half cycle 53 of the input voltage (47), the SCR 43 is ON through most of this half cycle, representing a heavy load condition. Conduction is triggered early, at trigger point 54 of approximately 30 degrees, and the output voltage 45 is increased. Thus, the output voltage 45 is regulated by varying the phase angle of the conduction trigger point.
In accordance with a first aspect of the invention, a power converter is provided, comprising an input, an output, a pass element connected between the input and output, and a controller that switches the pass element ON and OFF at phase angles of an AC input voltage received at the input in order to regulate a DC output voltage at the output. The input voltage may comprise a single or multi-phase signal.
In one embodiment, the controller switches the pass element ON at a first selected phase angle, and OFF at a second selected phase angle, the first and second phase angles determined by the controller based on the output voltage.
In one embodiment, the pass element comprises a pair of series-connected field effect transistors coupled source to source and operated in fully enhanced mode.
In one embodiment, the power converter comprises a plurality of pass elements connected between the input and output, the controller switching respective pass elements ON and OFF independent of each other, wherein the number of pass elements switched ON by the controller is based on the output voltage. In accordance with one aspect of this embodiment, the controller is preferably configured to determine the phase angles for switching the respective pass elements ON and OFF based at least in part on balancing current through the respective pass elements.
In accordance with another aspect of the invention, a method of regulating power using an AC to DC converter is provided, the power converter comprising an input, an output, and a pass element connected between the input and output, the method comprising switching the pass element ON and OFF at phase angles of an AC input voltage received at the input in order to regulate a DC output voltage at the output.
In one embodiment, the pass element is switched ON at a first selected phase angle, and switched OFF at a second selected phase angle, the first and second phase angles determined based on the output voltage.
In one embodiment, the converter comprises a plurality of pass elements connected between the input and output, the method further comprising switching respective pass elements ON and OFF independent of each other. In accordance with an aspect of this embodiment, the number of pass elements switched ON is based on the output voltage, and the phase angles for switching the respective pass elements ON and OFF is based at least in part on balancing current through the respective pass elements.
Other and further aspects and features of the invention and embodiments of the invention are shown and described in the accompanying figures and description thereof.